This invention relates to an apparatus for burning dry ultrafine coal (DUC), pulverized coal (PC), coal water fuel (CWF) and other liquid or gaseous fuels especially in applications for space and/or water heating.
In the past, cyclone type combustors have been widely used for large utility power plants. These devices generally consist of horizontal cylindrical combustion chambers wherein fuel and air are injected axially at the center or tangentially at the side of one end. Burning continues along the length of the combustor until exiting the opposite end.
Cyclone combustors are inherently high temperature devices which promote the formation of undesirable NO.sub.x and preclude the use of desirable limestone injection to remove SO.sub.x. In addition, these devices suffer from: relatively short particle residence time due to the straight through design; rapid decay of gas-gas and gas-particle mixing and reactions both along the combustor axis and towards the core region; and entrainment of fuel particles in the center exhaust region where combustion is severely limited due to low, local oxygen levels and poor mixing causing particles to quickly leave the combustor with the flue gas stream. As a result, extensive flue gas treatments are necessary to clean up the exhaust to an environmentally acceptable level.
Attempts have been made to improve the efficiency of cyclone type combustors by providing a horizontal double vortex configuration wherein fuel particles are entrained in a spiral flow path for maximum combustion and minimum particulate emission. Such a device is shown in U.S. Pat. No. 4,144,019.
Although providing an increased spiral flow path thereby increasing the residence time of a particle, these devices can neither retain a particle for sufficient lengths of time for complete burnout nor provide a controlled burning environment within the combustion chamber. As a result, these type cyclone combustors provide less-than-desirable performance in terms of combustion efficiency, firing intensity, operational flexibility, and pollution control.